The invention relates generally to fluid jetting systems and more particularly to constructions of jet heads that are easier to keep free of dust and other debris. An example of a fluid jet head in accordance with the invention is the print head of an ink jet printer.
Ink jet printers produce images on a substrate by ejecting ink drops unto the substrate in order to generate characters or images. Certain ink jet printers are of the xe2x80x9ccontinuousxe2x80x9d type where drops are ink of continuously jetted through an orifice of a print head in a charged state. The charged droplets of ink are then electrostatically directed onto the substrate when printing is desired and into a gutter when printing is not required. Another type of an ink jet printer is xe2x80x9con demandxe2x80x9d type ink jet printer. Drops of ink are selectively jetted through an orifice of a print head when printing is desired and not jetted when no printing is desired.
An ink storage chamber is commonly connected, via an ink flow passageway, to the print head, to provide a constant flow of ink to the head of the printer. Proper ink jetting generally involves capillary action between the ink and passageways in the ink jet head to position ink at the proper location in the head for proper jetting and drop formation. Thus, high pressure outside the print head can undesirably force ink back into the head, whereas low pressure outside the print head can undesirable draw ink out of the head. Build-up of material in the ink passageway can affect surface tension interactions and disrupt proper operation.
Thus if debris accumulates at surfaces of the ink jet orifices through which ink drops are jetted, ink can undesirably soak into the debris and undesirably accumulate and cause additional debris to be trapped at the orifice. This can alter the surface wetting properties at the orifice and inhibit proper ink droplet formation. Under extreme conditions, the build-up of debris can clog the orifice and prevent printing or lead to interrupted printing and/or streaking.
Certain ink jet printers can be used for high speed, high volume applications, such as canceling checks or postmarking mail, in which of tens of thousands or hundreds of thousands of pieces are passed by the print head in printing session. It will readily be appreciated that printing such a large volume of pieces will generate a considerable amount of dust and debris as the pieces are transported, in close proximity, past the print head.
Many ink jet heads are constructed to require purging, wiping and/or cleaning processes, to keep the orifices sufficiently clean. However, this can be an undesirable task. It also slows down and/or interrupts production.
U.S. Pat. No. 6,196,657, the contents of which are incorporated herein by reference, describes multi-fluidic cleaning for an ink jet print head. In certain embodiments of the invention, liquid cleaning solutions, such as alcohols or acids are used to clean the face of the print head.
It has also been proposed to blow and/or vacuum air over the print head surface to remove debris and liquid ink from the face of the print head. For example, manifold plates have been etched or formed with sheet metal to create vacuum ports and fins to direct air and vacuum across the print head orifices. This has been proposed in connection with flat-face print head and those in which the orifice is surrounded by a raised step structure. However, the designs have not proved to be fully satisfactory both in terms of effectiveness complexity of construction and durability.
Accordingly, it is desirable to provide an improved fluid jet head that is more easily kept free of debris or to otherwise overcome drawbacks of the prior art.
Generally speaking, in accordance with the invention, an improved fluid jet device and method of keeping a fluid jet head clean are provided. The face of the fluid jet head includes one or more orifices, through which fluid is jetted. The orifices are formed through convex ridges at the surface of head. In a preferred embodiment of the invention, the slope of the ridge from the orifice to the face is either generally constant or increasing, to provide the convex shaped ridge. In an embodiment of the invention, air is blown over the ridge and over the orifice, to keep dust and debris away from the orifice. The flow of air, the shape of the ridge and the proximity of material on which printing occurs can be constructed and arranged to provide laminar flow of air or other gas over the orifice. The downstream side of the ridge from the orifice can have a shallower slope than the upstream side. A vacuum port can be provided on the downstream side.
Accordingly, it is an object of the invention to provide an improved fluid jet head and method of keeping a fluid jet head clean, which overcomes drawbacks of prior systems.
The invention accordingly comprises the features of construction, combinations of elements, arrangements of parts and methods of operation, which will be exemplified in the constructions and methods hereinafter set forth, and the scope of the invention will be indicated in the claims.